1. Field of the Invention
This invention relates to an intrauterine contraceptive device, and more particularly to such a device which after initial expansion in the plane of the uterine cavity is locked to prevent further expansion but can contract upon contraction of the uterus.
2. Description of the Prior Art
As the effects of increased population become increasingly severe, resulting in environmental conditions which are deteriorating at an alarming rate, more and more effort is being placed on means for slowing the increase in world population, if not entirely halting such increase.
One type of contraception which has found considerable acceptance is the intrauterine contraceptive device, commonly known as an IUD. The IUD is a device which is placed inside the uterus, a soft tissue organ made primarily of smooth muscle. The way in which it operates to prevent pregnancy is not entirely understood but it is well known that any foreign body placed in the uterus has a contraceptive effect which is 90 to 95 percent effective. However, some such devices which have been used have caused the wall of the uterus to become eroded or partially penetrated causing pain and bleeding to the user, thereby necessitating removal. In many instances the IUD's are expelled from the uterus and this is believed to be because they are not fitted properly, such as being too small, or otherwise not constructed to resist expulsion. However, when larger IUD's are used, there is a greater instance of pain and bleeding and sometimes the IUD induces unwanted contractions of the uterus.
IUD's have been constructed in numerous shapes and sizes and of various materials, but each has had certain deficiencies. One IUD was made by injecting silastic into the uterus which then set up to form a cast. However, this procedure was abandoned because of the high incidence of expulsions, probably due to the distention of the uterus in the anterior-posterior diameter. A popular form of IUD is the Lippes Loop which is a sinusoidal spring-like device which is stretched into a linear shape and inserted into the uterus after which it contracts to fill the uterine cavity, but lies only in one plane namely the plane of the uterine cavity and does not significantly expand the cavity in the anterior-posterior diameter. However, the constant resilient force against the walls of the uterus may cause abrading of the walls and eventual bleeding and even perforation.
One attempt to overcome these problem is shown in applicant's U.S. Pat. No. 3,802,425 which issued Apr. 9, 1974. This patent discloses a number of IUD's which can be introduced into the uterus in collapsed condition and expanded until the uterus is substantially filled whereupon they are made rigid. Since these IUD's are rigid they will not cause constant pressure against the uterine wall and will resist expansion. However, upon contraction of the uterus the user of the device might experience greater than usual discomfort and pain since the IUD will not collapse upon contraction of the uterus. Sustained contractions could result in abrasion of the uterine walls or embedding therein possibly creating medical problems.
An IUD is disclosed in U.S. Pat. No. 3,659,596 to Robinson in which the expansion of collapsible legs of an IUD are limited by a membrane extending therebetween. However, unless the IUD is perfectly sized to the uterus the desired result of having the IUD completely fill the uterus without either embedding into the uterine walls or being too small to completely fill the uterus will not occur. If the IUD is too large, the legs thereof will not expand until the membrane interconnecting them is drawn taut. Thus, the legs will continue to exert pressure on the uterine wall which can result in abrasion and embedding. On the other hand, if the IUD is too small even after the legs of the IUD are expanded they will not completely fill the uterus in the plane of the uterus because of the limitations of the outward movement thereof by the interconnecting membrane. This small size of the IUD increases the chance of expulsion.